This invention relates to casting aluminum ingot, and more particularly, it relates to aluminum ingots having shaped ends.
In the vertical casting of aluminum ingot, a shallow depression is left on the top of the ingot because of shrinking during solidification. The bottom end of the ingot is generally flat. During rolling of the ingot, the surface layers in contact with the rolls undergo larger deformation than inner layers of the ingot. This results in the top shallow depression and the flat end being extended when the ingot is rolled in the reversing mill. This has the problem that the depression forms what is referred to in the industry as an “alligator” type split at the ends of the rolled material. Even if the top depression is removed, the alligator split still forms due to the nature of rolling. The alligator splits must be removed, and this results in scrap which is a significant factor in determining recovery rate of the ingot. If the depression is not removed, it can result in processing problems down the line. Thus, there is a great need for a method and system to solve this problem in order to increase the recovery of metal from the ingot.
In the past, several approaches have been used to resolve this problem. For example, U.S. Pat. No. 6,453,712 discloses a method and apparatus for reducing crop losses during slab and ingot rolling concerns the formation of a slab ingot having a specially configured or shaped butt end and optionally a head end as well. A special shape is formed by machining, forging or preferably by casting. The special shape at the butt end is imparted during casting by a specially shaped bottom block or starter block. The special shape of the bottom block is imparted to the cast ingot butt end. The specially shaped butt end of a slab shaped ingot is generally rectangular in shape and has longitudinally outwardly extending, enlarged portions, which slope downwardly toward a depressed central valley region. The lateral sides of the enlarged end portions and the depressed valley region carry transversely extending, tapered or curved edges. A similar shape may be imparted to the head end of the ingot at the conclusion of a casting run through the use of a specially shaped hot top mold or by way of machining or forging the cast head end. During subsequent hot rolling in a reversing roughing mill, the specially shaped slab ingot minimizes the formation of overlap and tongue so as to improve material recovery by reducing end crop losses and to increase rolling mill efficiency by increasing metal throughput in the mill.
U.S. Pat. No. 4,344,309 discloses a process which includes a method during slabbing, in which, recesses in the thicknesswise direction are formed on a pair of opposite surfaces at each end of the top and bottom of said steel ingot, subsequently, the central portions which have not been rolled, are rolled to the depth of said recesses, then, recesses in the widthwise direction are formed at the same end as described above, next, the central portions, which have not been rolled, are rolled to the depth of said recess in the widthwise direction; and, when the thicknesswise reduction value is ΔHT and the widthwise reduction value is ΔHW in said thicknesswise and widthwise reduction rollings, ΔHW/ΔHt is regulated to 0.40˜0.65 in a region where the material has a comparatively large thickness and the side profile of the material presents a double barrelling, and ΔHW/ΔHT is regulated to 0.3 or less in a region where the thickness of the material has a comparatively small thickness and the side profile of the material presents a single barrelling; whereby fishtails are prevented from growing so that crop loss consisting of fishtails and double-plate shaped overlaps can be reduced, thereby improving the rolling yield to a considerable extent.
U.S. Pat. No. 4,587,823 discloses an apparatus and method which makes possible the semicontinuous rolling of an extensive range of product widths from no more than three widths of slabs. The leading end of a slab is forged or upset laterally between dies tapered to reduce its width at said end gradually to a value less than the desired width at the end of the pass. The slab is then passed through grooved vertical edging rolls to reduce its width and into the rolls of a roughing stand. The edge rolling tends to move the overfilled metal into the void created by the dies. As the trailing end of the slab approaches the roughing stand the edging rolls are backed off, allowing that end of the slab to fan out laterally. As the slab leaves the roughing stand it is rolled between grooved vertical edging rolls to reduce spread and bring the fanned-out trailing end to size. That operation causes the trailing end to bulge rearwardly at its center, so compensating for fishtailing. The roughing stand is then reversed and the slab rerolled in the opposite direction in the same way.
U.S. Pat. No. 1,603,518 discloses a method of rolling ingots to avoid ears or cupped ends on the same which comprises providing an ingot having predetermined end dimensions, and predetermining the heat of the ingot and the depth of reduction relatively to the said end dimensions to cause the effective extrusion forces to be active over the total end area to move the end surface substantially uniformly relatively to the body of the ingot.
U.S. Pat. No. 4,608,850 discloses a method of operating a rolling mill in a manner that avoids the occurrence of alligatoring in a slab of metal as it is reduced in thickness in the mill. The slab is subject to a schedule of repeated passes through the mill to effect a predetermined amount of reduction in thickness of the slab in each pass. The method comprises the steps of analyzing the pass schedule of such a slab, and noting any pass in the schedule that has a combination of entry gauge and reduction draft that may subject the slab to alligatoring. An untapered nose of the slab is next presented to the bite of the mill, and if the combination of entry gauge and reduction draft is one that is not subject to alligatoring, the slab is passed through the mill to reduce its thickness as scheduled. However, if the combination of entry gauge and reduction draft is one that causes or tends to cause alligatoring in the slab, the method changes the size of the working gap of the mill by an amount that changes the combination of entry gauge and reduction draft to one that does not subject the slab to alligatoring. The nose of the slab is then directed to the bite of the mill having the changed working gap, and, once the nose of the slab has entered the bite of the mill, the working gap thereof is returned to the size that will effect the schedule reduction and thickness of the slab.
U.S. Pat. No. 4,593,551 discloses a method of reducing the thickness of a slab of metal under conditions that tend to produce alligator defects in the ends of the slab, the method comprising the steps of tapering at least one end of the slab and directing the same into a rolling mill. The tapered end of the slab is reduced in thickness in the mill, the amount of reduction increasing as the tapered end passes through the mill. The slab continues through the mill to reduce the thickness of the same. The end of the slab is again tapered and directed again through a rolling mill, with each of said tapers providing combinations of entry thickness to thickness reduction such that the reduction taken in the area of each taper is in an entry thickness to thickness reduction zone that does not produce alligatoring in the ends of the slab. The remaining untapered portion of the slab is reduced in thickness in the mill in an entry thickness to thickness reduction zone in which alligator formation tends to occur.
U.S. Pat. No. 4,387,586 discloses a method and apparatus for rolling a rolled material widthwise thereof wherein the rolled material in the form of a flat metal which may be a slab of metal having a large width as contrasted with the thickness has its lengthwise end portion shaped by compression working while the rolled material remains stationary in such a manner that the lengthwise end portion is formed with a progressively reducing width portion in which the width is progressively reduced in going toward the end of the rolled material, and a uniform width portion contiguous with the progressively reducing width portion and having a width equal to the minimum width of the progressively reducing width portion between its end contiguous with the progressively reducing width portion and the end of the rolled material. Thereafter, the rolled material is subjected to widthwise rolling, whereby the fishtail produced at the end of the rolled material can be greatly diminished.
In spite of the above, there is a great need for an economical process and system which resolves the problem of alligator splits to increase the recovery of metal from the ingot and to reduce scrap.